Rubber Rolling Mill Finds the Right Inverter

For more than a decade, a rubber rolling mill in the northwestern United States enjoyed great success using a 150-hp inverter on its main mill drive. With time, the drive eventually failed, introducing more than obvious problems. In seeking to replace the device, mill staff attempted to implement various new drives.

Staff

03/01/2003

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For more than a decade, a rubber rolling mill in the northwestern United States enjoyed great success using a 150-hp inverter on its main mill drive.

With time, the drive eventually failed, introducing more than obvious problems. In seeking to replace the device, mill staff attempted to implement various new drives. Unfortunately, none of them worked quite properly. The search continued until a suitable 150-hp, general-purpose open-loop unit was found.

At first, mill personnel thought that the new unit might not be large enough, especially since staff anticipated a higher output level in the near future. However, during a temporary hook-up, the drive—which was delivered the same day it was ordered—immediately proved itself. It did not stall or approach current limit during heavy press operations. Importantly, it powered through a "double-fold" test without stalling and only reached current limit for short, intermittent periods.

Then, an acid test was performed by "triple folding" the material. Even the mill's old drive couldn't do this; in the past when attempting this feat, the mill had to be stopped and reversed with the material being cut away. The new unit struggled but made it through the process.

The mill continued to run on the temporary 150-hp unit until a larger unit was delivered. The lesson learned was that hp rating—usually a major selling point with inverters—is not the only factor and that amps and overload ratings should be given equal consideration.